Radio identification system



7 Sept. 22, 1953 c. w. J OIV-INSTONE ET AL 2,653,234

RADIO IDENTIFICATION SYSTEM Filed 001.. 4, 1945 5 Sheets-Sheet 1 GATEDD.C. INTEGRATOR TRIG. BLOCKING AMP RESTORER TUBE MIXER CHARGING CATHODEDIODE -FOLLOWER AUDIO 0S0 FRUIT SQUELOH CATHODE FOLLOWER AUDIO OUTPUT3mm CHARLES W. JOHNSTONE WALTER N. DEAN LEONARD MAUTNER Sept. 22, 1953c. w. JOHNSTONE ET AL 2,653,234

RADIO IDENTIFICATION SYSTEM Filed Oct. 4, 1945 5 Sheets-Sheet 2 I05 U mln '07 |Q3 I04 (A) M W gmmwm E lG E CHARLES w. JOHNSTONE WALTER N. DEANLEONARD MAUTNE R Sept. 22, 1953 c. w. JOHNSTONE ET AL 2,653,234

RADIO IDENTIFICATION SYSTEM Filed Oct. 4, 1945 3 Sheets-Sheet 3 I UUU UILUIQUI ELIE- 5 (CONTINUED) Ewe/Mow CHARLES W. JOHNSTONE WALTER N. DEANLEONARD MAUTNER Patented Sept. 22, 1953 UNITE RADIO IDENTIFICATIONSYSTEM Application October 4, 1945, Serial No. 620,348

4 Claims. i

This invention relates to a circuit and method for producing apredetermined continuous output signal from a series of input signalshaving predetermined characteristics.

More particularly this invention relates to a circuit and method fordiscriminating in favor of discrete energy pulses having predeterminedcharacteristics and deriving from a series of such pulses apredetermined output signal which endures continuously substantially forthe duration of the series of discrete pulses.

In radiant energy location and identification systems, it is known totransmit pulses of energy and use the information derived from echoes todetermine the range and direction of targets from which the energypulses are reflected. It is also known to install in friendly craft orat friendly stations, a receiver-transmitter which responds to eachreceived energy pulse with a transmitted pulse of predeterminedcharacteristics whereby the interrogated craft or station may beidentified.

Under certain conditions it is desirable that the transponding craft, inaddition to identifying itself as friendly, be able to communicate withthe interrogating station. This invention will be described inconnection with an embodiment wherein the interrogating station includesa means for distinguishing between two types of answering pulses, asdetermined by the interrogated craft.

.In the circuit of this invention, answering pulses from an interrogatedcraft are applied at a. predetermined rate to the input of the circuit.The answering pulses are of two types, narrow and wide. The circuit ofthis invention discriminates in favor of the wide pulses; utilizes aseries of wide pulses to produce a continuing gate enduring for theduration of the series of wide pulses; and employs the gate to controlan audio generator producing a tone of predetermined frequency and ofduration dependent upon the duration of each incoming series of widepulses.

It will be understood that at the receivertransmitter or transpondor ofthe interrogated craft, a control means will be provided whereby theresponse may consist, selectively, of either a series of narrow pulses,which will produce only silence in the audio circuit at the receivingstation, or a series of wide pulses, which will produce either a .dot ora dash depending upon the durationcf the series of wide pulses.

This invention will now be particularly described with reference to theaccompanying drawings in which,

Fig. -1 illustrates a circuit embodying the principles of thisinvention; and

Fig. 2 illustrates certain wave forms appearin throughout the circuit ofFig. 1.

Referring to Fig. l, the circuit is shown consistingof input terminalIt, to which pulses from the receiver of the interrogator-responsor areapplied. The pulses are amplified in tube II by application to grid |2thereof. To suppressor I3 of tube l I is applied a controlling strobe,which will be more fully explained hereinafter. Output from amplifier ll is applied to grid I4 of tube I5 having anode l6 and cathode ll. Theoutput at anode I16, consisting of a rising saw tooth produced by the RCaction of resistor 2| and capacitor 22, is applied to grid 23 of tube24. The two anodes 25 and 26 of tube 24 are connected together, as arethe cathodes. Grid 30 of tube 24 cooperates with anode 26, through thecoupling of pulse transformer 3|, to produce a large output pulse inresponse to a relatively small triggering pulse. This will be recognizedas the known operation of a non-free-running. blocking oscillator.Output from the blocking oscillator is taken from winding 32 of pulsetransformer 3| and is applied to grid 33 of a cathode follower havingresistor .34 in the cathode circuit thereof. The other half of tube 35is used as a charging diode, producing a rising saw tooth on anode 36thereof. Output from anode illi is applied to grid 40 of tube 4| throughthe filtering action of resistor 42 and stray capacitance 43. Acontinuing gate signal is formed on anode 45 of tube 41, while asustained audio frequency signal is generated by the action of the otherhalf of tube 4| comprising anode 4.6 and cathode 41 acting as a modifiedHartley oscillator. I he frequency of oscillation is determined byinductor and capacitor 5|. This audio signal, appearing on cathode 52 oftube 4|, is applied to grid 53 of tube 54. The continuing gate appearingon anode 4.5 of tube 4| is applied, after amplification and inversion inthe other half of tube 54 having anode 55, .to grid 53 of tube 54.Output appearing on cathode 6 0 of tube 54 is applied thru a couplingcapacitor to output terminal 6 l.

The operation of the circuit of Fig. 1 will best be understood byreference to Fig. 2, illustrating wave forms throughout the circuit ofFig. 1. Reference letters (A) thru (L) in Fig. 2 indicate the voltagesat thecorrespondingly marked points in Fig. 1.

Referring now rto the drawings, Fig. 2(A) illustrates a signal such asmight be applied to terminal ill of the circuit of Fig. 1. Shaded pulsesmil. llll. N12, 6-3, and MM constitute the regularly spaced pulsesreturning from .an interrogated transpondor. Pulses 105, H16 and Ill!are random pulses, which will not be translated by the circuit becauseof the action of .a range strobe to be described hereinafter. It will benoted that pulses thru )3, inclusive, are wire, whereas pulse I06 isnarrow. As will be described hereinafter, the series of consecutive widepulses will produce an output signal which will cease with the cessationof the wide pulse series and the appearance of the narrow pulse seriesrepresented by 1114.

On the anode of tube I I will appear, amplified, the pulses I throughI04 inclusive, as shown in Fig. 2(B), while the intermediate random aswell as random pulses, will be blocked. The

strobe gate applied to suppressor I3 of tube II will appear on the anodethereof as a negative step or pedestal III] (Fig. 2(B)). Superimposed onthis negative pedestal will be the amplified input pulse I00, appearingas a negative pulse I I I. The other pulses of the system IIII, I02,I03, and I54, falling within a strobe gate, will likewise be amplifiedas shown in Fig. 2(B); whereas pulses I05, I56 and Iiil, lying outsidethe desired range, will not be translated.

Pulses III, on the anode of tube II, will be applied to grid I4 ofnormally conducting tube I5, causing it to cease conduction. Cessationof conduction in tube I5 will start a rising saw tooth wave on its anodeI5 through the action of RC circuit 2 I--22. The level from which sawtooth II3 starts to rise, 1. e., the level H2 in Fig. 2(C), isdetermined by the bias on cathode I! of tube I5, which is in turndetermined by the setting of potentiometer 55. Voltage appearing onanode I5 is applied directly to grid 23 of trigger tube 24, cathode 66of which is biased below the grid out 01f point. Therefore, until therising saw tooth II3 of Fig. 2(C) reaches a level II4, determined by thebias on cathode 65 and by the level of pedestal II2, no signal willappear on anode 25.

When rising saw tooth II3 has reached point I I5, equal to the out oillevel I I4, a negative pulse will start to appear on anodes 25 and 25 oftube 24, as shown at I in Fig. 2(D). This pulse will be appliedpositively through winding 32 of transformer 3! to grid 33 of cathodefollower 35. A positive pulse IZI, corresponding to pulse I20, willappear on cathode 3'! of tube 35. The overswing I22 associated with mainpulse I20 will be eliminated by the action of grid 33, biased to cut offwith respect to cathode 31 by the voltage divider action of resistors 34and 59.

Pulse I2I, appearing on cathode 31 of tube 35, is applied throughcapacitor II to the charging diode having anode 36 and cathode III. Thepositive excursion of pulse I2I will be largely damped by the diodeaction which ties point (F), to ground for positive excursions.Therefore, the signal at (F) will swing only slightly positive as shownat I23 in Fig. 2(F). The negative excursion terminating pulse I2I willbe faithfully reproduced at I24 by virtue of thelong time.

constant represented by capacitor II and resistor 12. Upon terminationof pulse I2I, point (F) will be left at a potential well below groundand will return exponentially toward ground along line I25 in Fig. 2(F).

The slightly positive excursion I23 will be filter damped by the actionof resistor 42 and distributed capacitance 43, so that at I25 (Fig. 2(G)grid 40 of tube 4! will be pulled well below the cut off level I31, andcurrent will cease to flow between cathode 52 and anode 45. Cut ofivoltage on grid 40 produces two effects, shown respectively, in Fig.2(H), representing voltage on anode 45, and in Fig. 2(1) representingvoltage at cathode 52.

Considering first the effect at cathode 52, blocking of current flowremoves the damping eifect from LC circuit 5I)5I, permitting the otherhalf of tube 4|, containing anode 46 and cathode 41, to operate as amodified Hartley audio oscillator, with inductor 55 and capacitor 5|being the frequency determining elements. The audio frequency signalappearing at (I) is applied through capacitor I3 to grid 53 of tube 54.

Normally tube 54 would translate the audio signal of Fig. 2(I) to itscathode GI), where it would appear on output terminal 6 I. To improvethe operation of the circuit, however, there is included a means foreliminating unlocked responses, called fruit in the art. Fruit responsesof the wide pulse character, similar to pulse I00 in Fig. 2(A),appearing within strobes III) of Fig. 2(B), would not be synchronizedwith the challenging station equipment, and only a few consecutive fruitpulses would appear within strobes I Ill. To avoid confusion which mightbe produced by the spurious, although short, audio signal resulting,means are provided for requiring that the series of pulses, I00 throughI03, endure at least for a predetermined time before an audio outputsignal will be derived from the circuit.

This desensitizing, or fruit squelch, operation is performed by tube 54,having anode 55 and cathode 15. The fruit squelch operation consists ofdifferentiating the long gating pulse (Fig. 2G0), produced on anode 45of tube 4|, in BC circuit BIB-I1 to produce the signal of Fig. 2(J). Thewaveform of Fig. 2(J) is then applied to grid 8| of tube 55, driving itbeyond saturation, and producing at anode 55 the negative pulse shown inFig. 2(K) enduring for the first part of the gating signal of Fig. 2(H).Superimposed on this signal is the audio signal I33 derived at (I). Inthis manner grid 53 is pulled well below cut oii, so that the firstportion of the audio frequency signal I35 (Fig. 2(K)) occurs well belowgrid cut off, represented by line I3I.

Accordingly, it is not until point I32 on the audio signal has beenreached, that any signal appears on cathode 55 of tube 54. From thispoint on, the audio signal rapidly rises to its steady state biasedvalue and appears as an output dot or dash, represented by I33 of Fig.2(L). In order to minimize the click. produced by the negative excursionH4 at the output terminals, the operating bias is not made sufficient tomaintain the audio signal completely above the cut off line I3I. Thisdistorts, to a certain extent, the audio output I33, but it will beunderstood that, if desired, a pure tone may be obtained simply byraising the operating bias of grid 53 of tube 54.

By the time the next pulse WI has been decoded to produce pulse I35 oncathode 31 of tube 35, as shown in Fig. 2(E), the rising saw tooth I35of Fig. 2(G) has risen closer to the tube conduction and cut off lineI3l. With the appearance of pulse I35, the voltage at (G) will riseslightly by virtue of the positive excursion I48 at (F) and then will bepulled down sharply to point I ll. It will again start to rise towardground potential, but it will be noted that at no time has the voltageat (G) risen above the cut off line I3'I of grid 40. Thus the continuinggate on anode 45 and the audio signal on cathode 52 will be unaffected,as shown in Fig. 2(H) and Fig. 2(I), respectively. Each succeeding widepulse I92 and H13 appearing within the strobes will pull down thepotential at point (G) in time to avoid having grid 45 rise above itsout ofi potential, thereby continuing the signals at (H) and (I).

Pulse 33 represents the last pulse appearing in the communication chainand is followed by narrow pulse 194, which, while part of theinterrogation and identification system, and therefore falling with astrobe signal, does not have the necessary width to actuate thecommunication circuit described herein. Pulse I04 does not endure longenough to allow the rising saw tooth I49 to reach the firing voltage H4of trigger grid 23. Therefore, blocking oscillator 24 will not betriggered, and there will be no pulse translated to pull down the risingwave form I43 of Fig. 2(G). When I43 reaches conduction potential 137 atpoint I44, the anode cathode circuit d5-52 will abruptly conduct,terminating the gate of Fig. 2(H) at I 45 and simultaneously stoppingoperation of the audio oscillator portion of tube 4|, so that the audiosignal of Fig. 2(1) ceases. At this point the audio output appearing at(L) also stops.

It will be noted that the other half of tube i5, having anode 90 andcathode 9|, has been used as a D. C. restorer for control grid I2 oftube H. The function of this tube is to prevent the D. C. bias on gridl2 from rising above the value C1 shown. This phenomenon might occurwith high repetition rate input pulses, which would raise the averagevalue of the voltage appearing on grid I2 thereby increasing in efiectthe D. C. bias. The D. C. restorer prohibits such a rise in D. C. gridbias.

From the above description it will be seen that there have beendescribed a method and circuit for producing a predetermined audiooutput signal in response to a series of pulses, each pulse being ofduration greater than a predetermined minimum. Further it will be seenthat means have been provided for desensitizing the output portion ofthe circuit for a predetermined time after the initiation of the seriesof pulses in order to prevent translation of spurious signals whichmight meet the coding requirements of the input portion of the circuit.

In this manner a pulse system using regularly spaced pulses of energymay have superimposed upon it an aditional commuication function withoutin any way affecting the fundamental operation of the basic pulsesystem.

Although we have shown and described certain specific embodiments of theinvention, we are fully aware of the many modifications possiblethereof. This invention is not to be restricted except insofar as isnecessitated by prior art and the spirit oi the appended claims.

What is claimed is:

1. A circuit for producing a predetermined output signal in response toa series of input pulse signals of predetermined duration, comprising: asawtooth wave generator effective to produce during the duration of aninput signal a wave form of changing amplitude, means responsive to aseries of output pulses from said sawtooth generator means to produce acontrol signal of a constant amplitude having a duration equal to thetime interval over which said series of output pulses from saidgenerator exists, a signal generator means, means connecting the outputof said sawtooth generator means to said signal generator means toproduce a output signal, and a squelch circuit connecting said constantamplitude pulse to said signal generator means effective a predeterminedtime after initiation of said constant amplitude pulse to commencetranslation of output signals from said signal generator.

2. A circuit for producin a predetermined output signal in response to aseries of input pulse signals of predetermined duration comprising a sawtooth Wave generator efiective to produce, during the duration of aninput signal, a Wave form of changing amplitude, a threshold clippermeans fed by said generator and effective when said Wave form hasreached a predetermined amplitude to produce an'output pulse, anintegrator circuit responsive to a series of said output pulses toproduce a gating pulse having a duration equal to the interval overwhich output pulses from said threshold clipper means exist and signalgenerator means operative during application of said gating pulse todeliver an output signal.

3. A circuit for producing a predetermined output signal in response toa series of input pulse signals of predetermined duration comprising asaw tooth Wave generator, effective to deliver, during the duration ofan input signal, a Wave form of changing amplitude, amplitude sensitivemeans fed by said generator and effective when said Wave form hasreached a predetermined amplitude to produce an output pulse, a tuberesponsive to a series of said output pulses to produce a continuousgating pulse, an output signal generator operative during applicationthereto of said gating puls to produce an output signal, and outputsignal translation means effective a predetermined time after initiationof said gating pulse to commence translation of output signals.

4. A circuit for producing a predetermined output signal in response toa series of input signals of predetermined duration, comprising a pulseduration discrimination circuit designed to pass pulses having aduration at least equal to said predetermined duration, means responsiveto a series of output pulses from said discrimination circuit to producea control signal of a. constant amplitude having a duration equal to thetime interval over which said series of output pulses from saiddiscriminator circuit ex-- ists, a signal generator means, meansconnecting the output of said discriminator circuit to said signalgenerator means to produce an output signal, and a squelch circuitconnecting said constant amplitude pulse to said signal generator meanseffective a predetermined time after initiation of said constantamplitude pulse to commence translation of output signals from saidsignal generator.

CHARLES W. J OHNSTONE. WALTER N. DEAN. LEONARD MAUTNER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,199,202 Hermann Apr. 30, 1940 2,211,942 White Aug. 20, 19402,359,447 Seeley Oct. 3, 1944 2,444,426 Busignies July 6, 1948 2,489,297Labin et a1. Nov. 1949 2,493,648 Watton et a1 Jan. 3, 1950

